It is a common occurrence for one individual to try and call another individual on the telephone but be unable to get through, i.e., progress to the point where the destination telephone is ringing. The most common situation is when the destination number is busy. For standard wired telephone numbers, this is generally the only reason why a call cannot be cellular telephones, however, the situation is more complex. In addition to simply being busy, a very significant percentage of cellular phones are normally unavailable.
A cellular telephone can be unavailable for many reasons including that the telephone is off, the battery is exhausted, or that the telephone is out of range or cannot receive a sufficiently strong signal. In addition, even when a cellular telephone is fully operational and receiving a strong signal, the telephone can still be unavailable due to a lack of available channels within the given cell.
Because of the inherent structure of cellular telephone systems, even if the central control system can determine if a cellular telephone is busy, it cannot easily distinguish between phones which are available or those which are not. Thus, when a call directed to a cellular telephone is initiated, the system might not know whether the call can be completed. Instead, it conducts a search for the destination cell by cell until it is found or the system gives up. If the destination is unavailable, a message to that effect is generally played for the calling party.
In response, the calling party might redial the number from time to time in hope that the receiving call party becomes available. This is a time-consuming process for the call initiator and also contributes a significant part to the load on the cellular system during the redials when the destination is unavailable due to all the futile redials, without any revenue to the cellular service provider. In many cases the party initiating the call will give up and abort after one ore more redials, depending on his desires and circumstances, and this will generally cause loss of revenue to the service provider.
Various systems have been implemented to address the situation when a calling party cannot immediately reach the destination number. For example, some telephone service providers offer services such as “Repeat Dialing” wherein when a busy signal is reached, the caller can request that the telephone system monitor the busy status of the destination and then inform the caller when the line is free. While suitable for wired telephone systems, conventional repeat dialing applications do not address the problems of unavailability when the destination is a cellular telephone. Thus, even if the system determines that a destination number is no longer busy, the system does not know why. As a result, the caller can be informed that the destination is free, only to find that even though the destination is no longer busy, the destination is not available because, for example, the destination is out of range, the telephone has been turned off, or there is insufficient capacity in the cell to establish the connection.
Some attempts have been made to address the problem of making connections to unavailable wireless telephones. For example, U.S. Pat. No. 5,794,143 to McCarthy et al. discloses a method and apparatus for ultimately completing telephone calls to unavailable wireless telephones. As described in the '143 patent, when a call to a wireless telephone cannot be completed, the system marks the destination number as being unavailable. The system then waits for the destination telephone to register itself within the network. After a registration is detected, the system notifies the caller that the destination telephone is available to receive calls. While the system and method of the '143 patent does serve to reduce number of times the caller must redial an initially unavailable destination, the system does not guarantee that a call to the destination will, in fact, go through after the caller is notified of the availability. This is because the system relies only on the registration of a telephone in a wireless network as a signal to retry the call.
Registration tells a wireless network when a telephone first enters the network. However, it conveys no information about whether the telephone remains in the network after registration. Thus, if a telephone is unavailable for one of the reasons previously mentioned, the controller in the '143 patent will still view the status of the telephone as “registered” and therefore believe that the phone can be reached and inform the caller accordingly. In reality, the actual status of a registered cellular telephone is undetermined because conditions can change after registration occurs which would prevent a call from being completed, such as the telephone losing signal or the battery running out. In addition, there are circumstances where a validly registered and active telephone can still be unavailable due to, e.g., insufficient resources. If an unreachable telephone is marked by the system as unavailable, the system will not return the telephone to the available condition until it receives a new registration. However, because this unreachable telephone is still registered, there is no need to re-register with the network and thus the '143 system could theoretically wait forever to receive a registration signal. In addition, the '143 system assumes that the caller is always reachable and makes no provision for situations where the caller's telephone is busy or otherwise unreachable.
More modern cellular telephone networks implement various “Intelligent Network” functionality which is designed to monitor the status of cellular devices. Intelligent networking has been implemented largely in conjunction with wireless messaging services to enable the system to monitor the activity of a cellular handset. Such a system is described in U.S. Pat. No. 6,058,303 to Åström et al. entitled “System and Method for Subscriber Activity Supervision.” However, as in the '143 system, the '303 system also relies on the registration condition of the cellular device to determine if it is reachable and thus suffers from the same problems as the '143 system discussed above regarding the instantaneous availability of the device within the network.
Accordingly, it is an object of the present invention to provide a method and system for notifying a caller that a previously unavailable cellular phone destination is available which avoids the false negatives and positives associated with a registration-based system.
It is a further object of the present invention to provide a method and system which notifies a caller that a previously unavailable cellular phone destination is available only when there are sufficient system resources to complete a call to the destination.